I have a late 2009 27" iMac (i5). Right now I have a LG 27" monitor as as second display hooked up using a mini display port to HDMI adapter. I wanted to add a third monitor (24" Dell, used vertically). Not sure if my iMac can support a third monitor. Can I do this and have it be a separate monitor without just cloning the other one? Would a USB to DVI adapter work, and has anyone had any luck with these? This is the one I'm looking at: http://www.amazon.com/gp/product/B00ANTCU9M/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=A1AMUYYA3CT6HJ Thanks for any input!